1. Field of the Invention
This invention relates to a thermal recording material and its production method, particularly relating to a high quality thermal recording material for a recording medium as medical applications and its production method.
2. Description of the Related Art
Use of thermal recording method offers many advantages. Some qualities which distinguish the thermal recording method include: (1) it does not require an image-developing process; (2) when using paper as a support, the support material quality resembles the quality of material similar to plain paper; (3) it is easy to handle; (4) its coloring density is high; (5) the recording device is simple, easy to use, highly reliable and cheap; (6) there is no noise during recording; and (7) it does not require maintenance. Therefore, recently the thermal recording method is developing in various fields. For example, its application has been expanded to the fields of facsimiles, printers, POS labels and the like.
Conventionally, the thermal recording materials used for thermal recording, utilize the reaction of electron-donating achromatic dyes with electron-accepting compounds, as well as the reaction of a diazo compound with a coupler, and so on.
In recent years, demand has risen for the development of thermal recording material with a thermal recording layer on a transparent support onto which one can directly record with a thermal head, for use in such applications as overhead projections and the direct viewing of images on light tables. Transparent thermal recording materials are increasingly receiving attention in the medical field for producing medical diagnostic imaging.
Such transparent recording material possesses excellent transparency, however its disadvantage is that sticking or noise tends to occur when the image is recorded with thermal recording equipment such as a thermal printer. High transmission density is required in medical uses of transparent thermal recording material, so the thermal energy applied by the thermal head is increased. The increased thermal energy aggravates certain problems, such as sticking, noise during recording, and wearing of the thermal head. In order to reduce sticking and noise, a protective layer comprising of pigment and a binder as main components is set on a thermal recording layer. In addition to the protective layer, other layers may be provided according as needed, such as a gas-blocking layer, an undercoating layer, an ultraviolet light filtering layer, and a light antireflection layer.
Two methods are known for providing these layers on a support is known. One method is by sequentially coating each layer on the support; another method involves multi-coating all the layers simultaneously with an exclusion die system. In both methods, prevention of interflow of the respective coated layers is necessary to produce a high quality thermal recording material. When interflow between coated layers occurs, the condition of the surface deteriorates and therefore it becomes impossible to produce high quality thermal recording material. Furthermore, in production of a thermal recording material, it is dried with a high-speed wind in a drying process in order to improve production efficiency, hence it suffers irregularity on the dried surface resulting in a deteriorated surface.
Particularly, when an image for medical diagnosis is produced using a transparent thermal recording material, it is impossible to accurately perform a diagnose is if an image cannot be clearly formed. Deterioration in the surface condition of the thermal recording material has adverse effects on an image being formed.